Cross-point memories are memories that use intersecting address lines, such as row and column lines, with an intervening memory element. Examples of cross-point memories include magnetoresistive random access memory (MRAM), resistive random access memory (RRAM), ferroelectric random access memory (FRAM), silicon oxide nitride oxide semiconductor memory, polymer memory, and phase-change memory.
The memory element for conventional cross-point memories may be programmed by varying the voltage across the memory element (e.g., phase-change memory), or by varying the polarity of the voltage across the memory element (e.g., MRAM and some RRAM).
RRAM devices use resistive switching memory elements as an electronic memory. One type of RRAM memory element utilizes a material that may be, in one application, electrically switched between a first resistive value and a second resistive value based on the polarity of a current through the memory element. For example, a current pulsed through the memory element in a first polarity may cause the memory element to comprise a first resistive value representing a 1, while a current pulsed through the same memory element in a second, opposite polarity may cause the memory element to comprise a second resistive value representing a 0.
MRAM devices store information as an orientation of a magnetization. One type of MRAM memory element utilizes a magnetic tunnel junction (MJT). An MJT is typically formed from two ferromagnetic plates, each of which is configured to hold a magnetic field, separated by a thin insulating layer. One of the two plates is typically a permanent magnet set to a particular polarity, and the other plate is typically configured with a magnetic field that will change polarity to match that of an external field. A memory element may be written by passing a current through wires placed just above and below the MTJ element. A current in one polarity results in a magnetic field of the other plate in a particular polarity, while a current in the opposite polarity results in a magnetic field of the other plate that is opposite to the particular polarity.